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Wednesday, November 23, 2005

On cavity wall insulation

Jeff Howell, the Sunday Telegraph’s resident builder, writes this week on the vexed subject of cavity wall insulation. Jeff is firmly in the non-believer camp: he reckons that cavities, if built empty, should be left empty because the original intention behind a cavity was to stop water penetrating from the external brick cladding through to the house. Well, that is what the cavity wall designers would have us believe.

But my researches tell me that the reason for the widespread adoption of the cavity wall design in the 1920s and 30s was nothing to do with builders wanting to improve construction standards. No, it was down to cost and speed. It was (and remains) much quicker and cheaper to build a single skin of brickwork separated by a cavity from a single skin of blockwork, than to build a double thickness brick-only wall, the way Victorians and Edwardians built brick houses. In today’s money, it costs around £50 per m2 to build a single skin of brickwork, about £20 per m2 to build a block wall, thus around £70 per m2 to combine the two around a cavity. In comparison, a solid double-skin brick wall is going to cost close to double a single skin one, i.e. £100 per m2. It’s a no-brainer. If you were a 1930s housebuilder, you would switch to cavity walls, and tell your customers you were doing it for their benefit.

What’s remarkable about the whole cavity wall story is just how useless the cavity has been. It’s only marginally better at keeping rain out of a house than solid brickwork. It seems to make little difference whether it gets filled with insulation or not. Wider cavities perform better than narrower ones and failure rates are highest where the rain falls the most: neither of these facts will startle you.

The question, which exercises Jeff so much, is whether you should or shouldn’t inject insulation into an empty cavity. The government is all in favour as it’s one simple and cost effective way of reducing carbon emissions. And there are tempting grants available for you to do this. Check out the Energy Savings Trust website . Jeff reckons it causes problems elsewhere, specifically making damp penetration problems more likely. His evidence is sketchy at best: he claims that he gets a bulging postbag when he writes on the subject from people who have suffered penetrating damp and condensation problems since having their cavities injected.

Jeff has a more specific beef than just compromising the cavity. He reckons that cavity wall installers’ favourite material is mineral wool because it’s cheap and it’s very quick to blow in. In fact, he writes that gangs can do five houses a day. And he also claims that the job is often rather poorly carried out. At five houses a day, I can quite believe that. This leads to a problem with voids, where they have missed bits of the cavity out, and slumping, where the mineral wool fails to hold its position. Both these will lead to cold spots. In fact work by Kingspan, the Irish insulation manufacturer, supports these claims. They have undertaken various thermographic studies that highlight the prevalence of cold spots inside cavities.

Now Jeff reckons that these cold spots are likely to cause condensation inside the house. I think he’s wrong. He writes because the house is now better insulated, the internal temperature can rise and with it, relative humidity. This means wall areas that are slightly cooler than the rest can be subject to condensation and black mould, which can give the impression of penetrating dampness.

Now why do I think his analysis is wrong? Because I think his analysis of how condensation forms is wrong. Condensation requires temperatures to fall below a dew point: in most modern homes, that dew point is around 12°C. It varies with the relative humidity levels but in most homes in winter the internal temperature is kept at around 20°C and the relative humidity sits at between 50% and 60%. This air: moisture mix hits its dew point at 12°C. Now increasing the temperature doesn’t of itself increase relative humidity: in fact, without adding more moisture, it does the reverse. It certainly doesn’t affect the dew point temperature. If you leave a room unheated and the temperature falls below 12°C, you will find condensation forming on the coldest surface, which is often the window. If there is a cold spot in the wall, maybe where the cavity wall installers have missed a bit, then, yes, there is every chance that condensation will form next to it. But it is not the cavity wall insulation that is causing the problem, it’s the low internal temperature. In fact, cavity wall insulation should improve the situation because the room temperature will stay higher for longer, because the heat loss characteristics of the room have been improved.

So what’s my advice regarding cavity wall insulation? I say, go for it. If the installers reckon it’s OK, then I really can’t see what the problem is. And if it’s not installed perfectly, it is still better than nothing. But I do agree with Jeff on one thing. I think mineral wool is the worst option for this work: I’d go for polystyrene beads, everytime.

114 Comments:

Jeff Howell was spot on when he said that cavities should be left clear to provide good ventilation.

Many older properties were built without vertical damp proof courses (VDPC) around windows and doorways because with adequate cavity ventilation it was unnecessary. Obviously when the cavity is filled with mineral fibre this is no longer the case.

The presence of mineral fibre also causes an increase in temperature differential across the cavity which results in condensation on the inside of the outside wall which in turn can lead dampness on the inside walls (without water penetration from outside).

From personal experience I can confirm that injecting mineral fibre into the cavity of properties which do not have VDPCs around the windows and doorways will result in dampness and ruined plaster within 10 years as dampness slowly migrates through the brickwork around the windows and doorways to the inside walls. In my case the manufactures guarantee was worthless because they claimed that the mineral fibre does not absorb water by capillary. They also refused to accept any responsibility for the failure to ensure that the property was suitable for mineral fibre insulation before it was installed and I am now left with a bill for approx. £3500 to rectify the problem.

I am considering seeking compensation through the courts but high legal costs may make action uneconomic. I guess that the manufacturer who issued the guarantee is well aware of this.

Am interested to find out how RHD got problem rectified. I have been writing to CIGA since 2005 and they have not yet come to look at the black mould which I have got not only around the window frames and all over the bathroom walls but also now in the bedrooms! I just want it rectrified but no builders will take the job on!

I had cavity walll insulation installed about 5 years ago. After seeing mould and a damp patch on the outside wall I found I had a leaking header tank valve. Which was discharging during the night when the water was at it's highest pressure.

Whilst the cause was the header tank valve, if there was no cavity insulation, or the cavity insulation had been without voids the damage would of been far less.

Voids in the insulation not only create cold spots but also allow the water to track over the cavityto the inside wall. No voids and there is a barrier against damp.

I got a friend with an endascope camera to look inside my cavities and there are not only voids but several areas where there is no insulation whatsoever, just a hole where it was supposed to have been installed.

My advice "If you do get cavity wall insulation installed, make sure the installer uses a thermal imaging camera to check for cold spots". Soon every home will need to have an eco survey before it can be sold.

I wonder how many homes will be like mine, after having it installed free on a British Gas grant.

Hi, have been following the debate on cavity wall insulation with some interest. Have recently had mine done (mineral fibre); no obvious problems but in one room a new 'mouldy' smell has appeared and cannot trace the source of this.

Now suspect problem area might be windows and unseen damp from penetration between wall and brick.No real signs of any damp though.

My questions. If you replace windows can you fit these vertical damp proof courses before installing new frames? I am thinking of replacing windows. Also was planning to replace with double glazed wooden frames. Might it then be better to replace with UVPC?

My problem was rectified by breaking out brickwork from around the windows and installing a VDPC. This appears to have been successful. Another but more costly alternative would have been to remove all Rockwool insulation from the cavities.

I would recommend that any problems are investigated by a qualified chartered surveyor (FRICS) before deciding on the best course of action. Builders would be more likely to tackle the problem if they were to act on the instructions of a suitably qualified surveyor.

I have found that installers suppliers and the BBA all support each other in denying that there are problems even when the evidence is overwhelming, therefore obtaining compensation is difficult. I have not given up and I am currently being assisted by my MP.

Unfortunately, my cavities were insulated before cover by an insurance backed guarantee became the norm. I would recommend free advice from Trading Standards if the supplier of an insurance backed guarantee did not provide the cover which they had been paid for.

Using polystyrene beads is fine until you want to do an alteration.Even puting in a new extactor fan can cause a huge quantity of the beads to come cascading out leaving a large triangle section of the wall above the fan empty and the room flooded with beads.

ANSWERSorry - I don’t recognise or agree with the conclusion drawn in the example. Plaster perishes around windows with and without CWI, through condensate or perhaps water penetration at the reveals. The condensate can be driven by any cold bridge such as the masonry, window, window frame etc. Lifestyle and property maintenance have an influence on the promulgation of the concern.

For the most part, cavity ventilation and vertical dpc’s are red herrings.

The Guarantee is against defect in workmanship or materials - but cannot underpin the performance of the building, since this is driven by a large number of factors outside of the influence of the CWI and installing firm.

Peter Dicks

Technical Director

Cavity Insulation Guarantee Agency

01525 853300

07973 211756

Sent: 26 October 2007 15:34

To: Peter Dicks

Subject: RE: Dampness Problems

QUESTION

I know of a case where mineral fibre was installed in a 1930s house and after about 8 years plaster started crumbling around the windows.

The cause of the problem was found to be lack of ventilation in the cavity. The house had a normal cavity wall and a normal horzontal damp proof course to stop rising damp. The structure was well maintained and in good condition.

However there was no vertical damp proof course around the windows because at the time of construction this was not mandatory. With good cavity ventilation this was not a problem but after the cavity insulation was installed this essential ventilation was lost and dampness crossed to the inner wall at the window reveals.

The problem was checked by a qualified surveyor and he found no faults other than a lack of cavity ventilation. The lack of VDPC was not consierdered to be a defect because it was in line the original design of the property and and not unusual in houses built around the 1930s.

The insulation supplier (who issued the guarantee) said that the problem was not due to a failure of the insulation and would not payout under the life of property guarantee.

We find your advice very interesting and helpful. We are thinking of having cavity wall insulation in our bungalow. We have condensation evidence at each corner of the bungalow and using dehumidifers to help the problem. We do not have air vents. We are not sure if there was originally and they have been taken away. Do you advise putting air vents before having cavity wall insulation or go ahead without them?

Can anybody help me. We have moved into a ground floor appartment(block of 2)there is no dampness. But I found a mould forming on clothes in the storage drawers under the bed in both bedrooms. We have an ensuite in 1 bedroom. We have installed a dehumidifer in the bedroom with the ensuite. Should we go for cavity wall insulation. The problem occurred in Sept. after the damp summer, and no heating on. We have not been in the property for a year yet.

Surely the original artical on this page is wrong in saying relative humidity will not increase with temperature unless you add more moisture. You will be adding moisture by living - use a dehumidifier to see how much - and warm air can hold more moisture than colder air. The moisture will hang round the coolest parts, usually where furniture reduces air circulation, and help mould grow.

my house is 17years old and we have just recently had the garage made into another room there is a room above the garage and both rooms are realy cold my father in law said we cant get cavity wall insulation because we have got insulation in the wall already but my question is how come them two rooms are so cold and if we could get cavity wall insulation do u think it would be benificial to us if not is there another insulation we could benefit from.

We are considering CWI because of alterations being carried out and building control have specified it. However what puzzles me is that claims are made that 35% of heat loss is through the walls but how can that be - when heat rises? I am personally convinced of the benefits of roof insulation but do wonder about CWI.

VENTILATION, VENTILATION, VENTILATION.I have worked on many properties over the years (new and listed) and the biggest problem that I have seen is lack of ventilation. Installing CWI takes away ventilation in your house and you need to provide an alternative route to release the moisture build up in the air. If you can rule out external water egress (rain penetration, leaking pipe etc.)then the mould and dampness within rooms and around windows is nearly always due to the lack of ventilation. The easiest solution is to open a window at least once a day to change the air (or after a shower/ bath / washing etc.) The next best is to install an extract fan. Building Control do not insist on trickle ventilators and extract fans to new houses for fun! CWI has sealed your house by wrapping a blanket around it. VENTILATE YOUR HOME. Who knows, it may even smell a bit better.

I had CWI installed at the same time as a new condensing boiler, and since then a damp patch has appeared on the outside wall at the DPC level, but only in 2 or 3 places around the house. This patch then spreads from the DPC towards the ground but almost dries before it reaches there. At DPC level the patch is about 1 metre wide, but gradually reduces to about 30 cm just at soil level, so the water is going down not up. I have had the plumbing, central heating and drains checked but they are all ok. Could this be due to a complete absence of airbricks for ventilation, or has anyone any ideas please?

My question is,Do I need CWI or not,I can get this done free because I am 81 but I have always had doubts about it.My friend who is a builder of long standing,will not entertain it because of ensuing damp problems.I have no damp in my bungalow at present so I am loath to have this done in case dampness is caused.

Are Housing Association landlords responsible for installing CWI at all? If not, how would this be dealt with re costs when I am the middle tenant? Does CWI reduce noise disturbance and if not,can anyone recommend soundproofing materials for a low income lady but not on benefits please. Thanks

Why is everyone obsessed with damp being caused by mineral fibre insulation? If you already have a problem with damp, it COULD make it worse. It's down to you, not the intaller, to get this sorted first. If you have no probs at time of installation, it is true that CWI can help to prevent damp. All these people who have "spoken to a mate who's a builder" drive me mad! You need to talk to an installation company (I work for one) before making a decision.

Cavity wall insulation causes an increase in condensation within the cavity and prevents natural ventilation within the cavity. The cavities are designed to be ventilated. If you prevent the cavity from performing its function as designed you take a risk to and the consequences cannot be blamed on the building.

Any installer will tell you that cavity wall insulation does not cause dampness and will claim that the installation is fully guaranteed. However, if you have a problem and try to make a claim then thed installer and CIGA will both say that you are not covered because the problem is due to faults in the house - funny these faults were not evident before the CWI went in. I speak from experience.

Cavity wall insulation causes an increase in condensation within the cavity and prevents natural ventilation within the cavity. The cavities are designed to be ventilated. If you prevent the cavity from performing its function as designed you take a risk and the consequences cannot be blamed on the building, it is a result of obstructing a design feature.

NoteThe supplier should ensure that the building is suitable before the CWI installed.

Any installer will tell you that cavity wall insulation does not cause dampness and will claim that the installation is fully guaranteed. However, if you have a problem and try to make a claim then it is a different storey. The installer and CIGA will both say that you are not covered because the problem is due to faults in the house - funny these faults were not evident at the time of survey before the CWI went in. I speak from experience.

In new houses the cavity is only partially filled and there is an air gap between the outer wall and the insulation. This is to ensure that the cavity condensation which forms on the outer wall does not saturate the insulation. The plastic drain vents below the DPC level are provided so that the condensation is drained to the outside and cannot collect in the bottom of the cavity.

In a fully filled cavity these drains will not provide ventilation because air movement is prevented by the insulation.

Whether or not retrofit cavity insulation will cause dampness is dependant upon the quality of the survey prior to installaion. Note: The installer will not look very hard for reasons to not install. In the case of a pre 1950 house the survey should be carried out by an independant chartered surveyor.

The CWI people came today and filled the cavities. I am grateful for the recent advice on the damp problem. The Technical Manager of the company said that if empty spots occur then the outer skin of the cavity wall will remain much colder than the filled areas, and that some condensation will occur at this cold spot on the outer skin. The water will seep down the outer skin and appear at DPC level.I will monitor the patches and keep you informed.Didz

My father has been trying to persuade me to have my have house CWId. I have been loathe to do so, mostly because in Devon, 3ft-thick walls do not prevent damp. We built our house and I remember the architect being very hot with the builders about pug being knocked off the wall ties. I have no damp problems, our windows are mahogany and in perfect condition after 20 yrs. At the time of building, we installed double insulation in the loft. My heating bills seem fair-to-good when comparing my house with others. Having spent 10 minutes reading this website, I'm NOT going to have it installed and hopefully all discussions can cease! Very many thanks to you all.

My father has been trying to persuade me to have my have house CWId. I have been loathe to do so, mostly because in Devon, 3ft-thick walls do not prevent damp. We built our house and I remember the architect being very hot with the builders about pug being knocked off the wall ties. I have no damp problems, our windows are mahogony and in perfect condition after 20 yrs. At the time of building, we installed double insultaion in the loft. My heating bills seem fair-good when comparing my house with others. Having spent 10 minutes reading this website, I'm NOT going to have it installed and hopefully all discussions can cease! Very many thanks to you all.

I hope the action taken cures your problem, but the theory seems a bit dubious. The effect of the insulation is to prevent heat from moving from inside the house to the outer skin of the cavity. Therefore, where the insulation is missing I would expect the outer skin to be warmer due to umimpeded radiation from within the house and therefore less likely to attract condensation.

i am an inspector for a cwi company,and all comments on here are right and wrong!some houses are and are not suitable for cwi.and also its all down to the way you live.. eg, 60 years ago a bungalow was bult with single glazed windows,virgin loft and 9 x 6 vents in every room.cold house!fast forward 60 years and... all vents sealed over with plaster and wallpaper.upvc double glazing with no trickle vents! 300mm insulation in loft and cwi,lady lives all year round with no windows open,house sweats to death! mould everywhere! inc pic frames!!so many arguments for and against this,i could go all night telling stories about this,but at the end of the day like anything theres a risk!? a good company will recognise if your house is suitable for cwi or not?but beware with the goverment throwing millions of grants at the green issue,everyone is out to make money regardless of the consequences for the sake of a quick buck!...it pains me! i'm chasing my tale constantley trying to train teams and surveyors to sign up and install suitable propertys!unfortunatley i'm on a loser most of the time,and this can be said for all!!! insulation companies

i recently applied to have cwi, house inspected then they started work only to stop after having done one wall - reason being that the cavity on the remaining two wall isn't wide enough.aside from the fact that the inspector should have spotted this, i can understand the problem with the use of flock, as it will not flow into the cavity as well as beads. i asked to have beads used for the remaining two walls, but was told that the cavity is too narrow for beads also. i have a suspition this may be a load of waffle as th ebloke who did the work said they no longer had the right equipment/machinery and i have had problems getting to even speak to the company. my question then is this a qenuine reason for not being able to fill with beads? (i have used beads for other things, so i know how well they flow!) my house is 1930's semi, on the cold side.

I remember a report, (30 years ago?),which looked into CWI and concluded that it was NOT recommended for properties in areas exposed to high winds and heavy rain (like Pembrokeshire for instance). All materials used seemed to have possible problems as previously mentioned for polystyrene beads attacking PVC and falling out of holes .Rockwool has been known to be colonised by ants as I guess glassfibre could be too and polyurethane foam as originally used sometimes gave rise to unhealthy fumes while setting and cracking leading to tracking due to movement in the cavity leaves. Perhaps it would be better to leave the cavity alone and insulate the interior wall surface.

I Have not seen any comments about the corrosion and failure of wall ties due to water on the inside of the outer skin of brickwork, which over the years can occur, especially with the galvanised wire "Butterfly" ties. The two walls are then no longer tied together across the cavity & expensive cutting out & refixing is essential to stop the walls bulging or cracking.

i was approached by a company a couple of days ago & said that they could do it for free as my wife receives certain benefits, the lad said he would leave further info through my door and gave me his mobile number scrawled on a scrap of paper. still waiting fo his 'info' but i sense that i have found the answers right here.i WON'T be having it done ,instead ,as i get round to redecorating ,i'll look into internal insulation.. p.s. my neighbours had their walls done last year and the cowboys siliconed the airbricks up!

The thermal conductivity of air is similar to the thermal conductivity of the material used to fill wall cavities, so the reduction in heat loss is not significant, and certainly not worth the risk of problems with damp. Insulate the loft to a depth of 200mm and forget about the wall cavity.

I commented a few weeks ago and have been very interested to receive comments as they are posted by email. Am still NOT going to have it done, although my father hasn't given up trying to persuade me, even after I forwarded a comment about having an ant problem caused by rockwool cwi: he has an ant problem but has not confirmed whether it was post-cwi....

I suppose you could argue that this website is geared towards the antis, but I feel we should think of it as being geared towards the sensible people who consider everything very carefully and are rather wary of promoters' claims!

I worked in the cavity wall industry for a number of years and have seen many many horror stories caused by the failure of cavity wall insualtion.So much so that we developed a technique for extracting the stuff from the wall and, started a company specialising in actually getting the stuff out of the cavity.We appear to be getting busier and busier.If the material in the wall becomes wet for any reason it has to come out asap to prevent severe damage to internal render and decor.It cannot dry as there is no air circulating in the cavity.

A friend of mine had his house cavity wall insulated at the same time as plastic double glazed windows. Within three months black mould formed underneath his windows. The answer, from the companies concerned, was to but a de-humidifier!As far as ventilation is concerned, the best method is an open fire and a chimney.

your all nuts! im the inpector that posted previously, the guy that said they where cowboys for sealing up cavity vents is very wrong,they become redundant once the cavity is filled and have to be made water tight,ie sealed! and as for the old builders myth of cavitys need air circulating,history lesson commences... pre cavitys were solid walls that typically every 5 courses had header bricks,someone came up with cavity wall in the late 1800's which used far less bricks tied together and was far far cheaper to construct some props suitable some not. read above comments and make your mind up,a good cavity properly filled will cause you no problems and will save you money

WE HAD ARE CAVITY WALLS DONE YEARS AGO AND HAVEING PROBLEMS NOW WITH UNDER THE WINDOW IN THE BEDROOM IT IS GOING BLACK THIS IS NOT A CAVATY WALL ON THE FRONT OF THE HOUSE WE HAVE A CONRETE PIECE UPSTAIRS AND DOWN UNDER THE WINDOW WHICH HAS PLASTER BOAREDS IN SIDE WE LOOSE ALL THE HEAT THREW THISGOSE COLD WHITH IN HALF HOUR OF HEATING GOING OF WE HAD THE PEOPLE OUT WHO DID WHEN WE PAID FOR IT BUT THIS IS NOT COVERED SO IN FACT WE ARE JUST HAS BAD OF CONTACTED WARM FRONT AND THIS IS NOT COVERED DO YOU NO ANYWAY WE ARE COVERED WE ARE MY HUSBAND 74 AND MY SELF 70 DOES THE GOVERMENT NOT HELP WITH THIS

Very useful comments. However I wish I really knew the truth about this CWI as I will also be respon sible for my neighbours property if we go ahead as she is in the flat underneath me so we both have to have cwi as one cannot have it in a flat alone as the walls go from the top of the building to the bottom so to speak.

Can anyone recommend an alternative to CWI. My house is made of Mundick Block (1940's) and despite having vents and no CWI the entire house is like a giant wet room with condensation and black mould. I try to find a compramise of keeping the family warm as well as leaving windows open for ventilation. CWI sounds like it may cause damage to the mundic so is there an alternative?

hi, we are currently building a new house and are torn between pumping the cavity or leaving it empty. i will be using an insulated plaster board on the inside of all external walls , approx 70mm. any advice would be greatful the cavity is only 75mm wide.

When the installer came to my house to instal cavity wall insulation (polystyrene beads glued), he told me that, in the two rooms with open wood burning fires I would need to have AIR VENTS installed in the outside walls. WHY is this??

i had my cavty walls insulated. thinking it would cut my heating bill down ,not true ,but ive had so meny problems since i had the cavty walls filled with beads .my wall wapper gone black in my bedroom under the bay window ,my creem curtains tie backs turned green .aslo my bathroom grout around the tiles all black . under all my window sills black spots .what a mess .im 70 gone .this as made me ill so stressed out trying 2 get it sorted out ,but no one can help me up 2 now ,i would like this all removed .my home as been well mentained and i never had any problems with any sort of damp till i had the cavty walls done ,bigest mistake i ever made .ciga did come and have a look at my problems ,said it was condencation ,so did the firm who installed it .i have traiding standres on my case .im sure i got voids as the beads are comeing out and some vent are sealed up .so my addvice to any one interested in cavty wall insolation .dont bother stay with what you got .empty cavty walls to let the air flow my gas bills havent changed still very high .so ive gained nothing ,just alot of stress and damage to my property

The comment below is right about thermal conductivity, but missed the important difference: the cooling effect from air circulation. For example, in an empty cavity, warm air from the lounge wall can circulate around the whole cavity and cool down. Best to trap the air from moving, like the loft insulation does, or a sweater on a person does.

"Anonymous said...

The thermal conductivity of air is similar to the thermal conductivity of the material used to fill wall cavities, so the reduction in heat loss is not significant, and certainly not worth the risk of problems with damp. Insulate the loft to a depth of 200mm and forget about the wall cavity."

I was thinking of having CWI but after reading the comments of people who have had this done, and the problems they have had, I will remain with my cavities.I found that a lot of the comments regarding the actual value in respect heat loss through the walls ( with or without CWI )to be correct, there is very little difference between having cavity walls or when you have had CWI. I found the only person that said anything slightly in favour of CWI was Peter Dicks Of CIGA who has a vested interest in promoting CWI, I deduce from his comments that CIGA only guarantee the work carried out, not the problems that may have occured after the CWI was installed, after all he probably would not have a job . In his words," The guarantee is against defect in workmanship or materials." No mention of how effective or not CWI is and no comments as to reasons why people have had problems with condensation after having CWI installed( I thought this guy was a technical director.) enough said!!

We have cavity wall insulation in a 1930s house and it was marked on the survey that it could harbour damp which would come through the walls as penetrating damp.

We have just started decorating a downstairs room and found there to be penetrating damp where the chminey breast is (we had the fireplace removed by builders before starting decorating).

The wall was previously in bad repair (render cracked and blown) and we had this fixed at the beginning of summer as well as having the chimney removed above the roofline, fireplaces blocked up and airbricks put in inside and out, top and bottom.

Anyhow, we had the wall replastered internally and first worried when the plaster took a long time to dry out in patches. I applied a mist coat of white emulsion yesterday and found today yellow patches in the suspect places which leads me to believe we definitely have a problem.

My concern is that damp has collected in the cavity wall insulation, probably from the gas fire that was there previously and now we have penetrating damp. Interestingly the areas that are affected are where the chimney breast is, suggesting it isn't water ingress as it would have to follow a very strange path to get to the affected areas.

Who is 'kc' that said he works for a company that removes CWI??I had an inspector from the firm that installed mineral fibre here today. We have damp under a bedroom window. Basically he said 'tough'. Not their problem. The wall gets driving rain. He said their product will stop moisture but not water from getting across the cavity???? Moisture but not water hey. That's a new one on me.We never had a survey, applied for it and was given a date for installation. That was it. The bedroom had been re-papered a few months before installation and there was no dampness anywhere then.So who will take it out??

I'd really like to know if Mark Brinkley, the author, has (or would have) CWI?

I had it put in 2 years ago, and the condensation and black mildew spots in my home since, are ridiculous :(I had the installer back out the other day and he gave me the same sorts of answers as everyone else has had, also adding that if my house was a new build, it'd have a bathroom and kitchen extractor fan, and window vents. But they knew my home wasnt a new build when they installed CWI, though it is only 20 years old.

CWI was a big mistake, my house was a warm house anyway.I would absolutely NOT recommend it - whats the point in putting stuff in thats meant to keep the house warmer, when you end up having to open all the windows for ventilation and to ease condensation?

wow after reading that little lot I definatley won't be getting CWI. I live in a 1930's semi detached house with an extension which was added 4 years ago. We have been considering CWI because the older part of the house is so much colder than the newer part which has the board insulation in the cavities as specified by building control.

You would assume that something that the government is encouraging us all to have - would be tested, safe, Just another reason to not trust our government!!!! Why am I not suprised!!!

As a retired surveyor I concur wholeheartedly with Jeff Howell.Retro fit CWI is a gamble that I personally would never take myself nor recommend without a thorough survey (not a salesperson/rep) of the individual property as to suitability or ancillary works required.And always ventilate your property - yes that means opening windows, or switching on the extractor fan if you are boiling the kettle or a saucepan, using a steam iron, having a shower/bath, drying clothes over a radiator - excess moisture MUST be removed from the building. Do not be hoodwinked by half baked "green" energy saving schemes, no matter how genuine (including Gov backed initiatives) they may appear - look for the motives, especially if political and be wary of so called insurance guaranteed CWI schemes.

Recently purchased a bungalow 'with potential for improvement'. Have consulted the local Building Inspector about creating an en-suite in part of a large bedroom. The new space, against an experiot wall, will need to comply with new insulation level requirements. He suggested CWI! He seems to be saying no insulation - no approvale for the en-suite!! Any ideas or advice from all your experience? Thanks

Put very simply, I have had a very bad experience with condensation and resulting mould since having cavity wall insulation 2 years ago. Like others I have found an ASTONISHING level of bias and misinformation from the installer, EAGA, CIGA and BBA, in trying to resolve it. I dont know how they sleep at night.Basically I would say on balance that it is generally a good idea as most of my neighbours have had it done without issue. However I am VERY disappointed in the way these professionals will blame ANYTHING for the sudden condensation of condensation whilst completely disregarding how the house managed to function perfectly for many years prior to their handiwork. If you are one of the percentage for whom it causes problems the way they treat you will add to the misery of regrouting your bathroom every 3 months, changing your shower curtain every 5 weeks and cleaning your windows down every morning in the winter, oh and of course living in a house which is now classified with a category 2 (damp) health hazard etc. etc. Still I have probably saved 3% on my heating bills so its not all doom and gloom!!!!

I have lived in a 70's built house from new , no cavity insulation and a minimum of loft insulation . From the first winter the bathroom would develop condensation and black mould would form in various places where there was no air movement . The grouting had to be scrubbed often to stop it turning black . In desperation i fitted a 4" extractor fan and every time a bath was run the fan turned on for an hour or so - problem sorted . Hope this helps those with bathroom problems .

i have for the last two years been considering having cwi ,i work in the building trade have done for 35 years and always remember a foremans remark to me 30 years ago that bricklayers shouldnt let any waste cement or wood cuttings fall down the cavity as anything touching both walls of the cavity was a possible bridge for damp carrying from outside wall to inner wall ,so i have always had my doubts with cwi as if the beads are installed without voids they will touch both walls hence my worry about moisture making its way into interior walls ,after reading these posts i will not be getting cavity wall insulation .thanks for all the posts ,i just dont think its worth the riski.

Whilst waiting for a CWI surveyer (who is now over an hour late) i have been reading the above comments as i had my doubts about CWI all along , when he gets here i will turn him away, Thanks for all the advice.

Oh dear, having read this info I think I now realise what is causing my damp and would appreciate any advice. I have a 1920's home and had CWI (fibre)and loft insulation done with a government grant about 3/4 years ago. At this point I had no damp issues. They had to come out twice as they hadnt fully filled the cavities (I was advised of this by a builer). I now have a large damp circle around my window and when the room becomes hot ie with the oven etc on and no ventilation I get damp circles all over my walls and chimney breast (which has been capped. I have kept this in check iwth a dehumidifier but there are stains on the walls. Can anyone advise my next course of action to get this fixed as I assume it will only get worse. From what I read there is no point in contacting CIGA. Also my next door neighbour has just been refused CWI as the Company advised her that these properties are just not suitable due to their age. I am a single mum and I am so frustrated that this has happened and am dreading how much it will potentially cost to fix. Hope I can get some constructive advice/comments. thanks

My house is about 13 years old - we moved in 8 years ago and from day one we have been troubled with damp (black mould) in the bedroom above the garage and the family room which is at the back of the garage. It looks and smells disguisting! I try to open the windows for an hour or two every day and always use the extractor fan when showering etc but to no avail! I assume, given the age of the house, that cavity wall insulation (boards) were installed as part of the build??? My husband has checked for leasks etc - all clear. Has anyone got any advice / ideas?????

One of the best ways to save electricity around the home to keep your home warmer in the cold months. A great way of doing this is to invest in insulation such as cavity wall. The carbon and eventual cost savings of insulating our homes is terrific and typical savings for cavity wall insulation for example is: * Typical cost: £250 * Typical carbon: 610kg * Typical payback: 2 years

What if you have an older 'solid wall' home. These can indeed be difficult and expensive to insulate, however there are methods other than external cladding.

Solid wall insulation can be performed in several ways, with the best being involving adding an extra layer to the inside face of exterior walls – either boards within a narrow wooden frame or a clever flexible material called Sempatap.Either way it is expensive, and the return on investment is longer, but the carbon savings are great. * Typical cost: £5,500 - £8,500 (internal) £10,500 - £14,500 (external) * Typical carbon: 2000kg * Typical payback: Varies, but normally at least 10 years

I am a tenant of a small detached cottage, with a bigger living area downstairs than upstairs. Downstairs has a sloping roof where there are no bedrooms above, there is no access into this space.I very much doubt there is any insulation at all in there.Upstairs due to the quantness of the cottage there are two apex's so there is no room for insulation inside there.What is more both bedrooms are open on all four sides.In the past 9 months it has cost me £1800 in Flogas, coal & logs.I have not even been warm. I have no option but to use Flogas due to my landlord signing an agreement with them.The windows are 1960s wooden, very draughty.My landlord will not spend any money on even the smallest problems with the property, so there is no use in asking his help.I love the seclusion and country location.The house is freezing in winter.I am a pensioner!I feel I shall have to leave.As for someone above mentioning an open fire, yes and it is a stright up chimney, which means 95% of the heat is lost up there.The kitchen cooker has no hood, there is a massive damp mark on the wall, getting bigger.Upstairs the bathroom has a fan it works on keeping the mould out of there.My bedroom always has condesation on the windows if not real frost & ice on the inside.The spare bedroom suffers the same with its windows, it is now developing black damp spots, even though only last year it was painted.Please advise, on loft insulation, how do I get it there, CWI, Log burning sove and secondary glazing.Anything please.I love the house in summer

To pensioner; if you are over 70, or claiming any benefit, such as Council Tax Benefit, ring 0800 512 012 for FREE loft insulation and, if applicable cavity wall insulation. This is for tenants as well as owners.

Cavity wall insulation (CWI): As a landlord I had CWI installed in 8 flats ten years ago. The only problem is condensation and black mould on window reveals in bathrooms and some bedrooms.I think the explanation is that the windows are set in the outer leaf of bricks and the innermost inch of the leaf forms the outermost part of the window reveal. As the outer leaf is now a lot colder than B4 we get condensation there. Also the windows are now double glazed (with trickle vents) so the outer leaf is now probably colder than the window glass, so is the first port of call for condensation.Not all tenants get this as some ventilate their flats properly.

Solution would be to insulate the reveals, or at least apply wider plastic decor strips so can more easily clean any mould off.

To Keira01: You need ventilation. You said:"when the room becomes hot ie with the oven etc on and no ventilation". The time to get rid of moisture is when it is being made, so when cooking, drying clothes or bathing open a window a SMALL amount and leave it open for a while after.The cause seems to be that the insulation has much reduced the flow of ventilation through the wall, so you need to replace it by opening windows just a crack. Any DIYer or handyman can easily install trickle vents in exiting windows, allowing you some secure ventilation with windows closed, tho when cooking etc you will still need to open the window a bit as well.

George. your PVC windows, like all modern windows have rubber sealing strips around them, unlike old windows which provide really good background ventilation when "closed". building regs recognise this in new homes and require trickle ventilators to offset it, but few people specify trickle vents when having replacement windows. You can either fit trickle vents, OR just pull out and cut away some of the rubber seals at the top of the window; remember there are inner AND outer seals.Cavity insulation will NOT help the condensation around the windows, see my earlier post; IT WILL ELIMINATE the condensation in the cupboard on an outside wall.

About 25 years ago my wife and I decided to have the cavity walls of our bungalow insulated with urea foam. All was well for a while, the house was much warmer and we were very pleased with the result. Our bungalow was brick built, rendered and painted with masonry paint.

About five years later I was mouching about and I noticed that the outer brick layer appeared to be damp. I chipped off some of the masonry paint and discovered tha most of the outer brick layer was very damp. As I was on the point of repainting the outside walls I phone the Dulux help line to ask for advice. I had a very helpful conversation with a gentleman who introduced me to the problem of interstitial condensation. He believed that water vapour was passing through the walls and as its temperature fell to the dew point, vapour condensed into water and was progressively making the walls wetter and wetter. The masonry paint on the outside was acting as a vapour barrier and was preventing escape of the condensed water.

The Dulux gentleman suggested one of two solutions. The first one was to install a vapour barrier on the inside walls with vinyl wallpaper being suitable. The second suggested solution was to strip all the paint from the outside walls and repaint with a cement based paint such as Snowcem.

WE went for the second solution, I stripped of all the masonry paint and used Snowcem and the walls looked fantastic. And did it work? it certainly did. After about two years our walls were dry again.

After this experience, I will never again retrospectively install cavity wall insulation. I will never ever buy a house that has had cavity wall insulation retropectively install. I will also never ever paint outside walls using masonry paint. Snowcem is wonderful, it looks fantastic, it is porous and it erodes gradually. You can repaint every five years or so without it getting thicker and thicker.

Our present house has modern construction with insulatin boards attached to the outside of the inner brick leaf together with an air gap of about 2 inches. We have no damp problems.

I hope my comments are of some use. I am certainly with Jeff Powell on this one

"Jeff Howell was spot on when he said that cavities should be left clear to provide good ventilation." I agree. Now that we are experiencing the effects of global warming, every effort to keep your place cool counts.

Hi. I have a Dormer house with brick walls up to the 1st floor on the gable ends. Above this brick line this 1965 house has horizontal wooden slats attached to the joists without any form of insulation. Can I insulate this by pumping in some form of free flowing insulation on the top - i.e remove the top slats and pour/pump it in? Companies dont seem to want to take this on. Surely all dormer gables in the UK are not insulated?

I found Jeff's article to be very clear and informative, it makes logical sense and everything he says is backed up. Why is mineral wool worse than poly beads then?...because it allows less penetrating damp? oh but I thought you were saying CWI doesn't cause penetrating damp...hmmm nice and biased, do you affiliate with people who sell poly bead insulation?

I lived in France for a few years and the houses were built of single thickness 200mm clay blocks with a sort of honeycomb within. These apparently allowed the moisture to evaporate within , and the inside was lined with polystyrene backed plasterboard dot and dabbed on as over here , or an additional skin of thin block was built on the inside with rockwool in the void.However all of the houses had what was called a VMC which is a permanently running extraction system which takes air from all rooms if necessary. This is in addition to standard bathroom and kitchen extraction systems. As they are installed suspended from the rafters there is no noise or hum and they were available from all DIY outlets for about £80. If I ever build my own house over here I will go over and get one!!!

The idea of installi8ng a cavity wall insulation is brilliant. However, it is a must to visit some trusts' energy websites. On the other hand, you can ask help from other people who had already undergone same process to ensure that you'll get the worth of your money.

we are getting our end terrace house roughcasted this year,and have thought about cwi insulation before its done,after reading the comments we are scared to go ahead with cwi,two many negative comments ,apart from firms pushing it and the green brigade,is there any positives????.

I am looking into cavity wall insulation for my third year project for university and currently looking into problems that have occurred with cavity wall insulation in dwellings, if you have had problems would you be so kindly and to email me on JonesAR8@cardiff.ac.uk to tell me about the issues you have had please?Many thanks

I am looking into cavity wall insulation for my third year project for university and currently looking into problems that have occurred with cavity wall insulation in dwellings, if you have had problems would you be so kindly and to email me on JonesAR8@cardiff.ac.uk to tell me about the issues you have had please?Many thanks

It is always important to ensure that the cavity wall has been installed correctly and properly. This will prevent leakage and possible breakage. This will also prevent leakage especially when the water is in it's highest pressure.

could i suggest to all of you who are seeking compensation from certain companies for these matters to form a co-operative law suit with a spread cost over many the individual fee should then be lower and you could then get scientific research carried out on all your properties simultaneousley

The crucial cause to wall dampness is not considering the water vapour diffusivity of the differing materials used for the wall construction:

Clay has a very high water vapour diffusivity, hence why old houses built with either clay brick monolithic walls or a clay brick inner shell of an air filled cavity wall tend to have no problems with condensation what-so-ever. The masonry will absorb moisture peaks and slowly release it to the outside through diffusion. Even in hybrid wall construction this will not be problem as long as you have a wall construction where the water vapour diffusivity increases to the outside or a ventilated cavity. If you fill in cavity with insulation the dew point will be moved to the interface between the insulation and outer wall shell, hence causing massive condensation. Now, if glass or mineral wool was used as insulation material the outer wall shell will act as a diffusion barrier as it has a higher resistance to diffusion than the insulation material. Furthermore, there not anymore a ventilated cavity present which will transport off the water. Hence the insulation material will literally become soaked with water (and looses with it all insulation properties).

Now polyurethane foam is practically impregnable by water, hence one will not have the problem of water back propagating through the insulation, but now the wall has been made impregnable to water vapour and one will have major condensation problems in the house itself. (To protect the inner wall, a damp proof course is advisable) Naturally, this condensation problem can be solved with the correct ventilation of least 0.4 complete air exchanges per hour, but achieving such high air ventilation rates without an ventilation system with heat recovery will make the house extremely droughty and cold...

You will get the same problem of inside condensation with all modern build UK houses as they all use construction techniques where the wall is practically impregnable to water vapour. Now, if you wanted to have a house with good insulation, no condensation problems and is cheap to build you will have to finally adopt in the UK modern building materials: Poroton clay blocks or Ytong aerated concrete blocks. A 300mm monolithic wall with those will already achieve a good U-value of 0.26 while allowing water vapour diffusion. My parents' 20 year old house built from these is better insulated than any standard house in England and the only problem we have with humidity is that it is too dry in the house...

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There are millions of homes in the UK that have issues with CWI. This is either because the wrong type of product was used. Namely blown fibre or it has been poorly installed which has created cold spots and other issues.